Signaling parameters are passed between the application and the SCCP task in the form of messages, which correlate with actual SCCP messages exchanged across the link. Messages are fixed format structures consisting of one or more parameters (referred to as information elements or IEs).
Parameters are fixed format structures consisting of one or more fields. Parameters that are optional in a message contain a flag indicating their presence or absence from the corresponding SCCP message.
Applications generate SCCP messages by allocating a message structure, populating the values and setting the present indicator for each optional parameter it wants to include in the message, and passing the message to the appropriate SCCP function.
Likewise, once received messages have been decoded into the fixed message format by NMS SCCP, the application can scan each parameter to determine if it was present in the SCCP protocol message and, if so, extract its field values.
The following structure simplifies applications by enabling them to operate on fixed format structures rather than the variable length and variable formats employed by the SCCP protocol. The following illustration shows an example of a message/parameter/field structure: